Sepsis refers to systemic inflammatory response syndrome (SIRS) caused by infections, and the infection sources include bacterial, fungi, viruses, parasites, etc. Sepsis often occurs in patients with severe diseases, such as severe burns, multiple traumas, and other patients after surgery. Sepsis can be divided into: sepsis, severe sepsis, and septic shock, according to the severity thereof. The incidence of sepsis is so high that there are more than 18 million cases of severe sepsis in the world, and 750,000 patients with sepsis in the United States each year, and the number is rising at an annual rate of 1.5%˜8.0%. Sepsis is a serious disease with a high mortality, and there are about 14,000 deaths in worldwide caused by complications of sepsis every day, 21.5 million deaths in the United States every year. According to a foreign epidemiological investigation, the mortality of sepsis has exceeded myocardial infarction, as the main cause of death for non-cardiac intensive patients in ICU. In recent years, although the anti-infection therapy and organ support technology have made considerable progress, the mortality of sepsis is still as high as 30% to 70%. The high cost and medical resource consumption for the sepsis treatment seriously impact the quality of human life and cause a great threat to human health.
Neutrophils play a key role in the defense against infection which are quickly mobilize from the bone marrow and congregated at the sites of inflammation after infection, and used for releasing proteolytic enzymes, reactive oxygen species, cytokines and other substances to clear pathogenic microorganisms. In this process, overreaction will cause body injury, severe cases may cause tissue and organ dysfunction or decline which lead to the present of severe sepsis or septic shock.
Neuronal migration protein Slit is an evolutionarily highly conserved secreted extracelluar matrix glycoprotein with a molecular weight of about 200 kD, which plays a guiding role for axon growth and neuronal migration. The Slit gene cloned in mammals has three members, slit1, slit2 and slit3, which is composed of an extracellular signal peptide at N-terminal, four leucine-rich repeats (LRRs), also named as D1-D4 domain, a plurality of EGF (epidermal growth factor)-like repeats (seven in Drosophilidae and nine in vertebrate), a laminin G-like domain and a cysteine-rich C-terminal region, and among which Slit-2 is the most important. Robo protein family, a receptor family of Slit, is a single-channel transmembrane receptor. Slit functions by binding with the Robo receptor, and the LRRs domain is a region for the binding of Slit protein with Robo receptor. At present, there are literatures reporting that Slit2 protein may inhibit migration of neutrophils.
Recent research shows that Slit protein plays a major role in angiogenesis, tumor cell migration, leukocyte chemotaxis, etc. In U.S. Pat. No. 8,399,404B2, Slit protein and nucleic acids are used for the treatment of platelet coagulation and other related disorders, and a vascular device using Slit protein coating and cells capable of expressing a Slit protein are also disclosed. Patent WO2009105457 discloses a method and composition for cancer diagnosis, research and therapy, involving Slit2 protein, a tumor marker, effectively used as a diagnostic marker and clinical target for prostate cancer.
Tole et al., through the study, have found that the Slit2 protein inhibits the migration of neutrophils by inhibiting actin filament formation and cell polarization induced by chemokines. (The axonal repellent, Slit2, inhibits directional migration of circulating neutrophils. J Leukoc Biol. 2009, 86(6):1403-15)
Hohenester has found that Slit-Robo interaction is formed by IG1 domain of Robo binding with D2 domain of slit (Structural insight into Slit-Robo signaling. Biochemical Society Transactions. 2008, 36: 251-256), therefore D2 domain is very important for the biology activity of Slit protein.
Chinese Patent CN201310150884.4 reports a fusion protein formed by D1-2 sequence of Slit2 protein prepared by using gene recombinant technology. The fusion protein helps LRR fold correctly and an active functional polypeptide form, which could be used for the research and application of Slit2 protein.
Protein drugs with a molecular weight less than 20 kD could be easily filtrated by glomerular in the metabolic process, leading to a short half-life in vivo. In order to achieve a therapeutic effect, a frequent or high dose administration is always required, which brings a great inconvenience to the patient. Human serum albumin (HSA) is a stable “inert” protein, and not easy to permeate through the glomerulus under normal physiological conditions with a half-life up to 14-21 days in serum, which can be used as a carrier binding with other factors in the blood including bioactive proteins, thereby maintaining or prolonging the bioactivity of other factors in vivo. It is an effective way to improve the half-life of small molecular peptides or protein drugs by the fusion of small molecular peptides or protein drugs with HSA. Compared with other methods, construction of a long-acting albumin fusion protein drug could avoid the complex chemical modification and processing, and thereby which could be easy to operate and have a better economic advantage.
In order to overcome the deficiencies in the prior art, the present invention provides a fusion protein for prophylaxis and/or treatment of sepsis and use thereof.